The present invention relates to a laser exposure apparatus, more in details, to a laser exposure apparatus for exposing an identification code attached to a wafer for carrying out history control or quality control for respective process in semiconductor fabricating steps or the like.
Conventionally, in fabricating steps of a liquid crystal panel, there has already been carried out history control or quality control for respective fabrication process by attaching an identification code to the liquid crystal panel. Two-dimensional codes or characters are used for the identification code and the two-dimensional codes or the characters are marked on a surface of the liquid crystal panel by exposing the surface to laser beam.
However, in the case of the liquid crystal panel, the liquid crystal panel per se is a comparatively large object and therefore, it is not necessary to reduce the identification code to be marked and the identification code does not become unreadable. However, in the case of a wafer dealt with in semiconductor fabricating steps, the wafer is a very small object and therefore, the identification code attached thereto is obliged to be very small. As a result, in reading the identification code, the identification code may become unreadable by a scanning type camera.
FIGS. 4A and 4B are explanatory views showing a situation when an identification code marked by a conventional laser exposure apparatus is read by a scanning type camera.
As shown by FIG. 4A, an identification code Mxe2x80x2 marked by a conventional laser exposure apparatus is formed by an aggregation of a number of circular dots dxe2x80x2. When the identification code Mxe2x80x2 comprising the aggregation of the circular dots dxe2x80x2 is read by a scanning type camera, a number of scanning lines A through E are scanned to cross the identification code Mxe2x80x2 to thereby discriminate portions of the black circular dots dxe2x80x2 from a white matrix portion.
However, as shown by FIG. 4B, although according to the scanning lines A and D searching vicinities of centers of the circular dots dxe2x80x2, signal levels received thereby correctly catch the identification code Mxe2x80x2, according to the scanning lines B, C and E searching portions deviated from the centers of the circular dots dxe2x80x2, as shown by broken lines, there appears noise nxe2x80x2 caused by a clearance formed between the two contiguous circular dots dxe2x80x2 in signal levels and there is a concern that the noise is erroneously recognized as if the white matrix were present.
Further, in the semiconductor fabricating steps, after marking the identification code on the wafer, a metal film may further be coated in later steps. When the metal film is provided in this way, as shown by FIG. 5A, black and white contrast of the circular dots dxe2x80x2 is remarkably deteriorated and therefore, the scanning lines A through E must read to catch contours of the circular dots dxe2x80x2 and signal levels thereof appear as shown by FIG. 5B. Also in this case, according to the signal levels provided from the scanning lines B. C and E, similar to the case of FIG. 4B, there appears the noise nxe2x80x2 caused by the clearance formed between the two contiguous circular dots dxe2x80x2 and therefore, the noise nxe2x80x2 similarly causes the erroneous recognition.
The noise n or nxe2x80x2 in FIG. 4 or FIG. 5 may be avoided by a filter processing or the like. However, by adding such a processing mechanism, there poses a problem that the cost is increased or a processing time period is taken.
It is an object of the invention to provide a laser exposure apparatus in which even when a very small identification code is attached to a very small object such as a wafer, there is enabled marking for improving reading recognizability of the identification code.
A laser exposure apparatus of the invention achieving the above described object is characterized in comprising a laser oscillator for oscillating a laser beam having a circular section, a beam expander for enlarging the laser beam oscillated from the laser oscillator, a square mask for shaping the laser beam having the circular section enlarged by the beam expander into a square section and an optical system for contracting the laser beam formed into the square section by the square mask.
In this way, the laser beam having the circular section oscillated from the laser oscillator is shaped into the laser beam having the square section by the square mask and therefore, an identification code comprising an aggregation of dots exposed by the laser beam, is not formed with a clearance between contiguous ones of the dots as in the case of the conventional circular dots. Therefore, noise caused by the clearance is not caused in a signal searched by a scanning line of a scanning type camera and the identification code can be recognized correctly.